The present invention is directed to an exhaust system monitor for internal combustion engines, and more particularly, concerns a method of monitoring exhaust gas flow and detecting leaks and undesired exhaust system back-pressure due to catalyst and/or exhaust component plugging.
There exists a need for rapidly evaluating the extent to which exhaust gas flowing through an exhaust system and its corresponding components is restricted. Exhaust gas flow restrictions can adversely affect engine performance in both gasoline and diesel engines. Exhaust gas after-treatment systems for diesel engines, in particular, are susceptible to exhaust gas flow restriction due to plugging, among other things. This is primarily a due to the harsh operating environments of diesel engines resulting from the levels of particulate matter produced during the combustion process. Mufflers, catalyst systems, and emissions components such as traps as well as other after-treatment systems can, over time, become plugged with particulate matter rendering them ineffective or, at least, less efficient. A potential for problems associated with plugging and/or restricted exhaust gas flow also exists for gasoline direct injected engines because of the potential for soot production, for example.
A simple exhaust system back pressure measurement provides a direct measure of the level of restriction within the exhaust system at a fixed engine operating condition, i.e., speed and load. However, during normal engine operation, the speed and load vary over a wide range making simple back-pressure measurements useless for evaluating the level of degradation of the exhaust system components. Although look-up tables can be developed for evaluating the level of degradation of the exhaust system components as it relates to exhaust system back-pressure, they require significant calibration efforts and consume significant memory resources within the electronic engine controller.
In addition to monitoring exhaust gas flow restrictions which may adversely affect engine performance, there exists a need to monitor the integrity of the exhaust system components themselves.
For example, leaks in exhaust system components such as mufflers or catalysts can adversely affect emissions control compliance.
It is an object of the present invention to provide an improved exhaust system monitor. Another object of the invention is to provide a method of rapidly evaluating the extent to which the exhaust gas flow through exhaust system components is restricted. Another object of the invention is to provide an exhaust system monitor capable of monitoring the integrity of exhaust system components.
According to the present invention, the foregoing and other objects and advantages are attained by a method of monitoring exhaust gas flow through an exhaust system of an internal combustion engine. The method comprises the steps of generating a flow efficiency value, comparing the flow efficiency value to a reference efficiency value, and if the reference efficiency value is exceed by a predetermined amount, then setting a flow fault indicator flag. In one aspect of the invention, the flow efficiency value is generated as a ratio of the magnitude of the exhaust gas flow restriction, and the mass flux through the engine. The magnitude of the exhaust gas flow restriction is represented by the pressure drop across the exhaust system, and the mass flux through the engine is determined as a function of the mass airflow rate and exhaust gas density.
In another aspect of the invention, a system for determining exhaust gas flow efficiency in an exhaust system of an internal combustion engine comprises a first pressure sensor in operative communication with ambient air for generating a barometric pressure value (Pamb); a second pressure sensor located within the exhaust system for generating an exhaust system pressure value (Pe); and a temperature sensor located within the exhaust system for generating an exhaust gas temperature value. The system further includes a mass airflow sensor located proximate the intake manifold of the engine for generating a mass airflow value (mi). An engine control unit for determining the exhaust gas flow efficiency is also included. The engine control unit includes a microprocessor programmed to generate a flow efficiency value (KE) as a function of the barometric pressure value, exhaust system pressure value, exhaust gas temperature value and mass airflow value.
One advantage of the present invention is that it eliminates the need to generate and store look-up tables related to exhaust system performance. Another advantage of the present invention is that it can identify leaks in exhaust system components and thereby improve emissions control compliance. Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.